Surface-treating apparatus and method

ABSTRACT

A SURFACE-TREATING APPARATUS AND METHOD, THE APPARATUS INCLUDING CENTRALLY-JOINTED RADIALLY-EXTENDING BLADES COMPRISING A FAN-SHAPED PLATE, A RESILIENT COMPRESSIBLE COIL SPRING, INTERPOSED BETWEEN THE BACK OF THE PLATE AND A ROTATABLE DIRVE SHAFT NON-ROTATABLY JOINTED TO THE PLATE THROUGH THE SPRING,A ND A HOUSING GENERALLY SURROUNDING ALL EXCEPT THE FRONT FACE OF THE RADIALLY-EXTENDING BLADES, THE HOUSING TERMINATING IN A HOLLOW HANDLE WHICH ROTATABLY CARRIES THE SHAFT. A STABILIZER ROD BRIDGES BETWEEN THE FREE END OF EACH BLADE AND THE SPRING. THE SHAFT IS POWERED BY A SUITABLE MOTOR, AND CLAMPING STRUCTURE ASSOCIATED WITH THE BLADE IS PROVIDED TO MAINTAIN SHEETS OF ABRASIVE OR OTHER SURFACE-TREATING MATERIAL IN TAUT   RELATION ACROSS THE FRONT FACE OF EACH BLADE. A DUST EGRESS APERTURE IS PREFERABLY PROVIDED IN THE HOUSING TO ACCOMMODATE CONNECTION OF A VACUUM TO CONTINUOUSLY REMOVE PARTICLES TREATED BY ACTION OF THE ABRASIVE MATERIAL ON A SURFACE. PREFERABLY AIR INGRESS PORTS EXIST IN THE PERIPHERY OF THE HOUSING ADJACENT THE FREE ENDS OF THE BLADES. PROCEDURALLY, THE BLADES YIELD FORE AND AFT AS NECESSARY TO FOLLOW WARIATIONS IN THE SURFACE BEING TREATED, WITH THE STABILIZER RODS EXERTING A RESTRAINING FORCE COUNTER TO THE INSTANTANEOUS FORE AND AFT MOTION OF THE BLADES.

NOV. 16, 1971 B, MILLER 3,619,954

SURFACE-TREATING APPARATUS AND METHOD Filed Feb. 7, 1969 2 Sheets-Shoot 1 lNvliN-TOR. BILLY G. MILLER ATTORNEY Nov. 16, 1971 B. G. MILLER 3,619,954

SURFACE-TREATING APPARATUS AND METHOD Filed Feb. 7, 1969 2 Sheets-Shoet 2 I (L 29 L m [guts J a 1. I08

INVENTOR. BILLY e. MILLER ATTORNEY United States Patent 3,619,954 SURFACE-TREATIN G APPARATUS AND METHOD Billy G. Miller, 1430 Lincoln,

Salt Lake City, Utah 84105 Filed Feb. 7, 1969, Ser. No. 797,481 Int. Cl. B24b 23/00 US. Cl. 51-170 T 11 Claims ABSTRACT OF THE DISCLOSURE A surface-treating apparatus and method, the apparatus including centrally-joined radially-extending blades comprising a fan-shaped plate, a resilient compressible coil spring, interposed between the back of the plate and a rotatable drive shaft non-rotatably joined to the plate through the spring, and a housing generally surrounding all except the front face of the radially-extending blades, the housing terminating in a hollow handle which rotatably carries the shaft. A stabilizer rod bridges between the free end of each blade and the spring. The shaft is powered by a suitable motor, and clamping structure associated with the blade is provided to maintain sheets of abrasive or other surface-treating material in taut relation across the front face of each blade. A dust egress aperture is preferably provided in the housing to accommodate connection of a vacuum to continuously remove particles treated by action of the abrasive material on a surface. Preferably air ingress ports exist in the periphery of the housing adjacent the free ends of the blades. Procedurally, the blades yield fore and aft as necessary to follow variations in the surface being treated, with the stabilizer rods exerting a restraining force counter to the instantaneous fore and aft motion of the blades.

The invention relates to a surface-treating apparatus and method and more particularly to an apparatus and method adapted for power sanding drywall joints and the like.

It is common in the construction industry to make walls and ceilings in a building by attaching drywall, or wall board sheets to wooden studs and joists. Thereafter, adjacent drywall sheets are normally joined together by cement and a strip of tape so that each entire wall or ceiling surface comprises a single surface, all the joints being essentially smooth and seamless.

The cementing procedure for joining adjacent drywall sheets normally includes (a) placing a layer of bedding cement in the crack that exists between initially placed, adjacent drywall sheets, (b) placing a flat strip of tape, such as Perfatape, over each such cement-filled crack and (c) spreading several layers of cement over the tape. When the final layer of cement dries, it is necessary to carefully sand or otherwise abrade the finishing cement and to feather the edge portions so that the finishing cement will blend into the adjacent drywall. Sanding of other layers of cement is also usually undertaken. The sanding and feathering procedures are normally a timeconsuming, tedious process.

The present invention comprises a novel surface-treating method and apparatus usable to significantly require only limited time and effort to achieve a superior finish on joints in drywall and related products. A presently preferred embodiment of the apparatus comprising the present invention provides a novel rotatable sanding plate comprising radially-extending blades which blades yield to the contour of the wall by action of a spring at the back of the plate but at the same time increased pressure is exerted on high spots on the surface and also decreased pressure is exerted on low spots and thus smoothly sands and feathers a layer of cement disposed over a strip of tape covering a joint between drywall sheets. Stabilizers, interposed between each blade and the spring, exert a force counter to the mentioned yielding action to provide the described pressure effect and to prevent overcorrection or vibration, which might injure the wall as by gouging. Evacuating structure is provided to remove dust and other fine particles resulting from the sanding procedure as soon as the particles are formed.

Therefore, it is a primary object of the present invention to provide a novel apparatus and method accommodating rapid, facile treating or finishing of surfaces.

It is another primary object of the present invention to provide an improved apparatus and method for sanding and feathering joints between drywall sheets.

It is another important object of the present invention to provide unique sanding structure comprising radiallyextending spring-mounted blades which advantageously exert greater transverse force on high spots than low spots on a surface.

It is also a significant object to novelly provide in surface-treating equipment a plurality of centrally-united stabilizer blades rotatable by power means through a common mounting spring.

Another and no less important object of the present invention is to provide novel evacuating structure in an abrading system for removing particles resulting from the abrading action.

One still further object of the present invention is to provide an improved surface-treating apparatus accommodating easy application of the desired amount of pressure against a selected surface.

It is another important object of the present invention to provide improved sandpaper holding structure which maintains sandpaper in an effective operating position.

These and other objects and features of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawings wherein:

FIG. 1 is an elevational cross-section of one presently preferred embodiment of the invention, portions of which are shown diagrammatically;

FIG. 2 is a top plan view of the sanding plate of the apparatus of FIG. 1;

FIG. 3 is a top plan view of another presently preferred sanding plate configuration used in connection with the apparatus of FIG. 1;

FIG. 4 schematically illustrates a fragmentary longitudinal cross-sectional view of another presently preferred embodiment of sanding plate which may be used with the apparatus illustrated in FIG. 1;

FIG. 5 is an enlarged transverse cross-sectional view of one presently preferred embodiment of sanding blade comprising part of the sanding plate used with the apparatus of FIG. 1;

FIG. 6 is an enlarged plan view of a retaining clip used with the embodiment of FIG. 5;

FIG. 7 is a fragmenary top plan view of another presently preferred sandpaper retaining structure embodiment with parts broken away for clarity;

FIG. 8 is a fragmentary cross-sectional view taken along line 8-8 of FIG. 7;

FIG. 9 is a horizontal cross-section taken along lines 9-9 of FIG. 1;

FIG. 10 is a top plan view of a presently preferred housing embodiment of the present invention for use at corner joints;

FIG. 11 is a fragmentary side elevation viewed along lines 11'11 of FIG. 10;

FIG. 12 illustrates the general way in which the apparatus illustrated in FIG. 1 is used; and

FIG. 13 illustrates, with exaggeration, how one of the blades of the rotating plate yields to the contour of the exterior surface of a joint and how the stabilizer bar provides a counter force.

Referring now to FIG. 1, one presently preferred surface-treating apparatus, generally designated 20, comprises a surface-treating or sanding plate, generally designated 22, comprising a substantially planar support 24, preferably formed of rigid metal. The illustrated support 24 has upwardly projecting side edges 48 and 50 comprising portions of the sandpaper retainer 46, which will be subsequently more fully described. One presently preferred configuration of the sanding plate 22 is best illustrated in FIG. 2. The plate 22 is illustrated as having radially projecting arms or blades 28 and 30, the inward or back face of the planar support 24 being illustrated in the figure. The ends 27 and 29 of the blades 28 and 30 respectively are illustrated as being arcuately shaped and define the outer surface-treating limit of the blades 28 and 30.

An annular anchor plate 80 is welded to the back surface of the sanding plate 22. The lower support disc 80 is connected to a helical compression spring 82 by, for example, spot welding. The spring 82, best illustrated in FIG. 9, is preferably formed of a substantially flat resilient metal. The essentially flat cross-sectional configuration of the spring material limits distortion of the spring 82 primarily caused by the torque of the plate 22 as it rotates and also provides a desired level of resistance to compression. The spring 82 is also preferably centrally provided with a transverse reinforcing bar 84 which is welded at respective ends 81 and 83 to the spring 82 and which also inhibits undesired spring distortion due to the mentioned torque.

The upper trailing edge of the spring 82 is welded or otherwise permanently attached to the generally annular face plate 88. The face plate 88 presents an upwardly projecting boss 90 having an internally threaded bore 89 which is adapted to receive the threaded leading end 91 of a drive shaft 92. Thus, the spring 82 serves as a flexible connector between the shaft 92 and the plate 22.

The face plate 88 is joined to looped ends 117 and 119 (FIG. 2) of stabilizing bars 94 and 96 by screws 98 and 100. When at rest, the stabilizing bars 94 and 96 fit loosely through apertures 102 and 104 respectively located in vertical legs 113 and 115 of brackets 106 and 108, which brackets are welded or otherwise suitably secured to the back face of the plate 24. The stabilizing bars 94 and 96 are movable in axial and lateral directions within the apertures 102 and 104.

Thus, if one blade of the sanding plate 24 passes over a high spot on a surface being sanded as shown in FIG. 13, the spring 86 will be compressed on the side adjacent the stabilizing bar 96 causing the bar to exert a force on the bracket 108 counter to the movement of the blade to thereby counteract or stabilize blade displacement to prevent vibration or chatter at the plate 24. At the same time pressure on the high spot is increased by the mentioned action. Naturally, the spring 86 Will expand on the side adjacent the stabilizing rod 94 as also shown in FIG. 13, causing the rod 94 to exert an upward lifting force on the bracket 106 and attached blade 30.

The described undulating effect, accommodated by the coil spring 86, provides for excellent control of the sanding plate such that the blade action will not cause the abrasive material carried by the blades to cut into or gouge the wall, or the tape or cement at a joint. Restated, the blade with abrasive material will ride smoothly but firmly over high spots to make the joint surface even and precisely feathered at the edges of the cement 142 (FIGS. 12 and 13).

It is presently preferred that the cushion 26 or the cushion portions 42 function as backing for sandpaper or other suitable abrading material. The resilient cushion accommodates a more uniform sanding action and contributes to the avoidance of marring or otherwise damaging the drywall.

lf desired, the con-figuration of sanding plate illustrated in FIG. 3 and generally designated 32 could be used. The sanding plate 32 comprises arms or blades 34, 36, 38, and 40, each disposed in the same plane at 90 intervals. Each blade 34, 36, 38, and 40, has an arcuately shaped edge 33, 35, 37, and 39 respectively which, similar to the ends 27 and 29 above mentioned, define the outer surface-treating limit of the blades 34, 36, 38, and 40, respectively. A disc 89, situated upon a compression spring (not shown) above the sanding plate 32 is essentially the same as the disc 88 above, except disc 89 is attached by screws 91 to four radially projecting stabilizing bars 93, 95, 97, and 99 which are respectively received by brackets 101, 103, 185, and 107 each fixed by welding to the plate 32 adjacent the respective edges 35, 37, 39, and 33 thereof. The action of the blades, spring and stabilizer bars are the same as heretofore described.

Both sanding plate embodiments of FIGS. 2 and 3 are provided with a resilient cushion 26 shown as covering the entire leading face of each sanding plate 22 or 32. The solid pad or cushion appears to be best for initial sanding where roughness is at a maximum. If desired, cushion portions 42 may be disposed only on the outward surface of the arms or blades 28, and 38, or 34, 36, 38, and 40 (FIG. 4) thereby defining a central slot or recess 41 on the leading face of each plate 22 or 32. The spaced pairs of pads or cushions appears to be best for final finish sanding where a delicately feathered edge and even joint surface is paramount.

The cushion 26 and cushion portions 42 present a yieldable backing for sandpaper or other abrading material so that gouging and marring of a surface by the rigid support 24 is alleviated.

The sandpaper or other abrasive material could be adhesively secured to the cushion, or alternatively, could be physically restrained in taut relation across the cushion.

In this regard, FIG. 5 illustrates a presently preferred sandpaper holding structure adapted to be used with the sanding blade embodiments illustrated in FIGS. 1-4. It should be understood that similar structure could exist on the plate 32.

In FIG. 5, two substantially identical sandpaper holding structures are each generally designated 46. Each sandpaper holding structure 46 comprises peripheral flanges 48 and 50, respectively, which are continuous with the planar support 24 as previously mentioned and which are directed upwardly and inwardly as illustrated in the figure. Centrally disposed projections 52 and 54 are integrally attached to the planar support 24, for example by welding, and are directed upwardly and outwardly so as to oppose the flanges 48 and 5t respectively. If desired, the projections 52 and 54 may comprise a single upstanding projection (not shown) presenting an exterior shape adapted to Oppose the flanges 48 and 50.

A clip 56 (FIG. 6), preferably formed of spring steel or other suitably yieldable material with memory, is adapted to be received between the flange 48 and the projection 52 and, similarly, an identical clip 56 is adapted to be received between the flange 50 and projection 54. The clip 56 is essentially U-shaped suitably sized so that, when assembled, the horizontal portion 57 urges the ends 59 outwardly to exert a lateral force against the flanges 48 and 50 and projections 52 and 54. Thus, when it is desired to place a sandpaper strip 44 adjacent the cushion 26, a portion of the sandpaper strip 44 is placed initially over one flange 48 or 50 and, thereafter, the clip 56 is placed so that the ends 59 thereof exert a compression force on the edge of the sandpaper between the end 59 of the clip 56 and the flange 48 or 50. The sandpaper is thereafter tightly wrapped around the cushion 26 so that the abrasive side faces outwardly and is folded over the opposite flange 48 or 50 and similarly tightly held in place 'by another clip 56. It should be apparent that the sandpaper retainer 46 could also be used in like manner with the plate embodiments of FIGS. 2 and 3, except only one clip, larger in size, would be interposed between sandpaper ends next to flanges 48 and 50.

Another presently preferred sandpaper retainer embodiment, generally designated 58 and which may be used with the blade embodiments of either FIG. 2 or FIG. 3, is illustrated in FIGS. 7 and 8. With reference to FIG. 7, the planar support 24 is illustrated as being provided with centrally disposed, upstanding brackets 60 and 62 (FIG. 8) connected together with a longitudinally disposed shaft 64. The shaft 64 carries two opposed rotatable levers 66 and 68 which are each pivotally attached by pins 67 and 69 to arms 70 and 72. Arms 70 and 72 are pivotally connected to respective central portions 71 and 73 of clips 74 and 76. The clips 74 and 76 are preferably formed of spring steel or other suitable resilient material and are generally U-shaped, the respective terminal ends 75 and 77 being provided with a reverse curve or curl to present a smooth surface to the edge portions 48 and 50.

The operation of the sandpaper retaining clip 58 is illustrated best in FIG. 8. With reference to FIG. 8, the clip 76 is placed in initially open position as illustrated in dotted lines by manually arcuately rotating the lever 66 to the position illustrated in dotted lines in the figure. The arms 70 pivotally connected thereto will cause the clip 76"to be retracted away from the flange 50 of the sanding blade 22. Sandpaper 44 may then be placed around the edge portion 50 and the lever 66 depressed from the dotted line position in the figure to the solid line position. When the lever 66 and the attached arm 70 are in the solid line position in FIG. 8, a laterally directed force will be exerted on the clip 76 which resiliently urges the ends 77 thereof tightly against the flange 50 and thereby securely retains the sandpaper 44 adjacent thereto. The sandpaper 44 may be then tightly wrapped around the cushion 26 and attached to the flange 48 by the clip 74 in a manner substantially identical to that set forth for clip 76.

The surface-treating structure of this invention, as illustrated in FIG. 1, is preferably provided with an exterior housing 110, desirably formed of a lightweight material such as resin-impregnated fiberglass. The housing 110 is preferably cylindrical in shape and peripherally opens at a plurality of locations along edge 112 adjacent the surface-contacting cushion 26 of the blade 22. The housing 110 is provided with attached spaced roller assemblies 114 located at intervals. Intervals of 60 are satisfactory, though other spacing could be used. The roller assemblies 114 comprise rotatable wheels or rollers 156 carried by hearings or the like (not shown) upon axle 158. The axle 158 is disposed between fingers of a bracket 160 which is fastened to a vertical shaft 162.

A bearing sleeve 164 is fixedly connected to a U-shaped support 166 and circumscribes the shaft 162 so that the shaft 162 is rotatable therein. The support 166 is attached at the central portion thereof to housing 110 by a rivet 168. Although the wheel 156 and connected shaft 162 are rotatable within the sleeve 164, the retaining disc 170 prevents axial displacement of the shaft 162 out of the sleeve 164. The rollers 114 permit the housing 110 to be readily displaced over an essentially flat surface, such as a drywall surface 138 (FIG. 12), the edge 112 of the housing 110 being maintained slightly above the drywall surface by the rollers 114.

The housing 110 terminates in a centrally disposed hollow handle 116 which is fastened to boss 117 and is adapted to carry drive shaft 92 coaxially within the hollow thereof and powered by a suitable motor 132. The hollow handle 116 is provided with bearings 118 and 120 which are maintained in the handle with snap rings (not shown), connected exterior of and in a conventional way 6 to hearing retainers 119 nd 121 which are, in turn, attached to the handle 116 in press-fit relation. The bearings 118 and accommodate rotation of the drive shaft 92 and also accommodate axial displacement of the drive shaft 92 for a purpose which will be subsequently more fully described.

The housing 110 at boss 117 is further provided with an eccentric aperture 122 into which a hollow tube 124 has been fastened. The hollow tube 124 is coupled to a flexible tubing 126 which is connected to a conventional vacuum schematically shown and identified by the numeral 128. When the vacuum 128 is in operation, particles sanded from the drywall by the rotating sanding plate 22 accumulate within the housing 110 and are evacuated through the tube 124 and the tubing 126.

When finishing cement between sections of drywall is being sanded, most of the particles removed from the housing 110 will comprise the finishing cement. I have found that the particles may be collected in the vacuum and reused as finishing cement. Thus, a substantial savings in material costs may be provided.

The housing 110 may be provided with a plurality of peripherally disposed slots 130 to allow air to flow into the housing 110 to carry resulting particles into the vacuum 128. If desired, the slots 130 may be omitted and spaced annular recesses (not shown) may be located in the edge 112 of the housing 110 thereby accomplishing the same result.

The vacuum 128 and the drive shaft 92 may both be operated by the same prime mover 132, such as an electric motor or the like.

It is presently preferred that the drive shaft 92 be connected at its trailing end 134 to a hand-operated prime mover, such as a hand drill 136 or the like (FIG. 12). Conventional hand drills are provided with a bit chuck which securely receives the trailing end 134 of the drive shaft 92 and provides for easy control of the speed of the sanding blade 22. The hand-operated drill 136 further accommodates selective axial displacement of the drive shaft 92 relative to the handle 116 for manual application of a desired amount of pressure on the sanding plate 22.

In the operation of the surface-treating apparatus 20, the operation of the sanding plate 22 will be discussed, although it is to be appreciated that the operation of plate 32 is essentially identical therewith and, therefore, need not be separately described. Initially, sandpaper is attached adjacent the cushion 26 of the sanding plate 22 by securing it in tight-fitting relation around the cushion 26 in the manner previously described. A hand-controlled motor structure 132, such as a hand drill 136, is attached to the trailing end 134 of the drive shaft 92 and the hollow handle 116 is held in the one hand 143 of the user 140 while the drill 136 is held in the other hand as illustrated in FIG. 12. The vacuum 128 is actuated to continuously draw air and dust particles from around the sanding plate 22 while the sanding plate 22 is rotated. The housing 110 is placed adjacent the drywall 138 or other surface to be treated so that the joint 142 formed by finishing cement between adjacent drywall sections 144 and 146 is epxosed to the sanding plate 22, as illustrated in FIG. 12. The rollers 114 accommodate movement of the housing over the surface 138.

The sanding operation begins when the drive shaft is rotated by energy from the prime mover 132 and, thereafter, the operator 140 may selectively exert an axial force on the drive shaft 92 to control the pressure of the sanding plate against the cement joint to achieve the desired smooth or even finish on the seam 42 and, similarly, to feather the edges around the finished seam 142, so as to present a smooth contour with the adjacent drywall. Any force exerted axially along the drive shaft will be communicated to the plate 22 and the force will be exerted through the blades 28 and 30 in greater amounts to high spots than low spots in the surface 142. Thus, unevenness in the surface 142 is smoothed and marring is avoided.

When it is desired to treat corners, the housing embodiment 148 illustrated in FIGS. and 11 may be used. The housing 148 illustrated in FIG. 10 is similar to the housing 110 illustrated in FIG. 1 with the vacuum tubing 126 removed, the corresponding parts having the same numerical designations. The housing embodiment 148 in FIG. 10 differs from the embodiment 110 of FIG. 1 in that the embodiment of FIG. 10 is provided with a cutaway portion 150 adapted to be disposed at a corner joint adjacent a wall or ceiling which projects essentially normal to the surface being sanded. Rollers 152 which are oriented perpendicular to the surface being sanded and are adapted to ride against and space the cut-away portion of the housing slightly away from the wall or ceiling normal to the surface being sanded. The rollers 152 are each rotatably carried upon a pin 153 vertically disposed in a bracket 154 which is secured to the housing 148 with screws 155 and 157. The rollers 152 accommodate smooth, easy movement along the wall situated normal to the surface to be treated. The edges 27 and 29 of the sanding blades 28 and 30, respectively, are adapted to pass adjacent the open edge 150 as illustrated in FIG. 11 so that the open edge 150 is slightly inside of the outer limit reached by the edges 27 and 29 of the blades 28 and 30. Thus, corner locations where two walls meet may be rapidly and easily smoothed.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. In a surface-treating apparatus comprising a plurality of radially extending blades normally disposed in a common plane and permanently joined one to another at a common juncture so that each blade can yield out of said common plane in respect to the other blades as irregularities in a surface being treated are encountered;

a resilient connecting means comprising a coiled spring the axis of which extends normal to the plane of the blades, the base of the spring being permanently nonrotatably fastened at one end to the common juncture at the back side thereof;

a drive shaft having an axis essentially common with the axis of the spring when in its normal position, the drive shaft being permanently non-rotatably connected at one end to the other end of the shaft, the other end of the drive shaft being exposed for manual application of axial pressure thereto;

a housing surrounding essentially all of the resilient connecting means and the blades, except the front or surface-treating side of the blades;

bearing means disposed in a central bore of the housing between the housing and the drive shaft and accommodating axial to and fro manually induced motion of the shaft as well as motor induced rotation of the shaft;

spacing means carried by the housing which are placed contiguous with the surface being treated and causing the housing to be spaced a narrow distance from said surface.

2. In an apparatus of the type defined in claim 1 wherein the housing comprises a dome-shaped shield provided with (a) a hollow exhaust passageway accommodating vacuum removal of dust particles produced during surface treatment and (b) peripheral intake vents adjacent the spacing means for facilitating an influx of air to cooperate in carrying away the dust particles.

3. In an apparatus of the type defined in claim 1 wherein the spacing means comprises castor means which support the housing in said spaced relation from the surface being treated and allow the housing to move smoothly and easily over the surface being treated.

4. Apparatus as defined in claim 1 wherein the coiled spring is flat in its cross sectional configuration.

5. In an apparatus of the type defined in claim 1 further comprising a stabilizer bar interposed between the spring adjacent the shaft and each blade adjacent the distal end thereof to exert a stabilizing force counter to the direction of yield of the associated blade to a given surface irregularity commensurate with the adjacent compression or expansion of the spring caused by said yielding of the blade.

6. In a surface-treating apparatus comprising exterior housing means presenting centrally-disposed hollow handle means; shaft means rotatably carried internally within the handle means for relative axial displacement; blade means disposed generally normal to the axis of the shaft means and substantially within the housing means; and connector means interposed between the blade means and the shaft means which transfer rotation and axial displacement from the shaft means to the blade means but not to the housing means and the handle means.

7. In an apparatus of the type defined in claim 3 further comprising at least one collection container adapted to collect the removed dust particles for subsequent reuse as a cement base.

8. In an apparatus of the type defined in claim 6 wherein said blade means have a generally fiat surface-engaging face at least a portion of which carries a yieldable elastomeric cushion, the blade means being adapted to accommodate attachment of surface-treating material adjacent the elastomeric cushion.

9. In an apparatus of the type defined in claim 8 Wherein the central portion of the face is not covered by elastomeric cushion.

10. In an apparatus of the type defined in claim 6 wherein said connector means comprises a coil spring connected at one end thereof to the shaft means and at the other end thereof to the blade means and stabilizing bars connecting the one end of the compression spring to peripheral extremities of the blade means (a) to minimize vibration of the blade means during rotation thereof and (b) to concurrently exert increased pressure on high spots on the surface and exert proportionately decreased pressure on opposite low spots.

11. In an apparatus of the type defined in claim 10 wherein said spring comprises a centrally-disposed transverse bar joining spaced portions of the spring to alleviate spring distortion due to torque.

References Cited UNITED STATES PATENTS 2,612,648 10/1952 Lagant 51-180 UX 1,800,341 4/1931 Davies 51-180 X 1,622,592 3/1927 Kratz 51-1702 3,361,044 1/1968 Wolf et a1 51-177 X FOREIGN PATENTS 129,155 7/1947 Australia 15-49 R 629,586 8/1927 France 5-1702 JAMES L. JONES, 111., Primary Examiner U.S. Cl. X.R. 15-28, 49 

